Brush holder for dynamoelectric machines



8, 1959 e. GARTNER ETAL 2,900,540

BRUSH HOLDER FOR DYNAMOELECTRIC MACHINES Filed Nov. 7, 1956 Fig.2.

Fig.3. Fig

INVENTORS Q I 5 G'linter Gcirtne'r, August Schwub I I and Hermann Horz.

ATTOR. EY

United States Patent BRUSH HOLDER FOR DYNAMOELECTRIC MACHINES Giinter Giirtner, Berlin-Weidmannslust, and August Schwab and Hermann Harz, Berlin-Siemensstadt, Germany, assignors to Siemens-Schuckertwerke Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Application November 7, 1956, Serial No. 620,927

3 Claims. (Cl. 310-246) The present invention relates to a brush holder for dynamoelectric machines and more particularly to a brush holder having a constant force brush biasing spring.

Brush wear, as well as commutator wear, is accelerated by excessive friction caused by unnecessary hig h brush pressure. Lower pressures give poor contact, causing sparking, heating, and increased electrical wear. It can be seen, therefore, that there is an optimum brush pressure at which the combined brush wear due to poor electrical contact and due to excessive friction is a minimum. Since, in conventional types of springs, the force varies with the deflection of the spring, the pressure on the brush'varies with brush wear. Therefore, this optimum pressure utilizing a conventional spring cannot be maintained. It is the usual practice to overstress the brush spring on new machines. As the brush material wears, the contact pressure decreases. For a short period the brush pressure is at the optimum value, and as the brush vcontinues to wear, the contact pressure decreases, and

electrical wear increases. When arcing occurs, the conventional brush is then adjusted to increase brush pressure. This adjustment introduces human error and at best this may provide the optimum value of brush pressure for only brief periods.

To avoid this excessive brush wear, it is desirable to provide a constant force brush spring which is initially adjusted to exert less brush pressure consistent with good contact between the brush and the commutator or slip ring.

The principal object of the invention is to provide a brush holder for dynamoelectric machines which can be manufactured at low cost, is simple in construction, and which will provide constant brush pressure for the life of the brush.

Another object of this invention is to provide a brush holder having a constant force spring for applying pressure to the brush which spring will require no adjustment.

A further object of the invention is to provide a brush holder having a constant force spring which will reduce electrical and mechanical wear of the brush material to a minimum.

Other objects and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawing in which:

Figure 1 is a perspective view of a transversely curved flat spring;

Fig. 2 is a perspective view of a transversely curved flat spring bent in a contrary sense;

Fig. 3 is a perspective view of a transversely curved flat spring bent in a normal sense;

Fig. 4 is a side elevation of the spring disclosed in. this invention;

Fig. 5 is a graphical representation showing the dependence of the loading of the free end of the spring upon the spring deflection; and

Fig. 6 is a perspective view of an embodiment of the brush holder of this invention.

ICC

The brush holder shown in the drawing includes a substantially rectangular-shaped brush support 10 having a rectanglular-shaped longitudinal opening 12 formed therein. Received in the longitudinal opening is a brush 14 arranged for longitudinal movement within the longitudinal opening 12. Secured at one side of the brush holder 10 are a pair of vertical-extending arms 16. Arms 16 extend upwardly a substantial distance above brush holder 10. Arms 16 are parallel to each other. Each of the arms 16 are bent perpendicular to their longitudinal axes adjacent their upper ends. The bent portions extend toward each other and are in overlapping relationship and slightly separated to provide an open- 'ing for the reception of an end of a leg 18 of a U-shaped spring 20. U-shaped spring 20 is secured between bent portions 17 by welding, brazing or in any suitable manner.

The U-shaped spring 20 is formed from fiat spring steel stock having a transverse curvature of radius r, as shown in Fig. 1. Spring 20 is bent longitudinally into a U-shape either in a sense contrary to the transverse curvature, as shown in Fig. 2, or in the same sense as the transverse curvature, as shown in Fig. 3. Spring 20 is bent longitudinally beyond its buckling point. The longitudinal radius of curvature a, Fig. 4, should be equal to the transverse radius of curvature r. Fig. 5 illustrates the result of a spring such as 20 being curved transversely and bent beyond its buckling point. The ordinate P represents the loading of such a spring. The abscissa S represents the deflection of the free end of the spring. It will be noted that the load P in the hypercritical range, which is to the right of the buckling point S starting approximately at 8,, is substantially independent of the spring deflection S. Spring 20 is designed to operate in the hypercritical range to the right of point 8,, so that as brush 14 wears down, the pressure exerted by spring 20 thereon will remain constant.

To the end of the free leg 22 of spring 20 is secured by any suitable means a pressure piece 24. The spring pressure produced by the transversely curved U-shaped spring 20 is conveyed over the pressure piece 24 to the brush 14. If desired, brush 14 may be formed at its upper end with a depression corresponding to the shape of pressure piece 24. The pressure piece 24 may be made of an insulating material in which case the current supply is carried by a copper wire directly connected to the brush 14. In special cases, the pressure piece 24 can be designed as a conducting contact piece. In this case the current supply can be carried by a copper wire connected to the spring 20. Because of its substantially large surface, the transversely curved U-shaped spring 20 provides a satisfactory cooling of the contact point.

Certain modifications of the brush holder, not shown in the drawing, can obviously be made. For example, it is possible to obtain a clearance free guiding of the brush in the brush holder by a slight inclination of the supporting of the bent portions 17 which would exert over the pressure piece 24 a transverse force preferably in a peripheral direction. The bent portions 17 can also be inclined in such a manner that a certain pressure will be exerted in tangential direction so that the brush will bear against a wall of the brush holder. In some cases this will secure a smoother operation of the brush.

It should now be apparent that a brush holder has been provided which is of simple construction which can be readily produced at minimum cost. As previously pointed out, a constant force is applied to the brush throughout the life of the brush. No adjustment is required to maintain optimum brush pressure.

A preferred embodiment of the invention has been shown and described for the purpose of illustration, but it will be apparent that various modifications may be 9 made, and it is to be understood that the invention in its broadest aspects is not limited to the specific details of construction shown but includes all equal embodiments and modifications which come within the scope of the invention.

We claim as our invention:

1. A brush holder for dynamoelectric machines, said brush holder comprising a brush support having a longitudinal opening formed therein adapted to have a brush arranged therein for longitudinal movement toward the periphery of a substantially cylindrical rotating member, a brush biasing means including a transversely curved, U-shaped fiat spring, said U-shaped spring being longitudinally curved beyond its buckling point, the initial radius of curvature of said transverse curve and the radius of curvature of said longitudinal curve being substantially the same, spring support means secured to said brush support and extending vertically upward from said brush support, one leg of said U-shaped fiat spring being secured to the upper end of said spring support, a pressure piece secured to the other leg of said U-shaped spring, said pressure piece overlying said brush and bearing thereon to urge said brush toward the periphery of said rotating member whereby constant pressure is applied to the brush throughout its useful life.

2. A brush holder for dynamoelectric machines, said brush holder comprising a brush support having a longitudinal opening formed therein adapted to have a brush arranged therein for longitudinal movement toward the periphery of a substantially cylindrical rotating member, a brush biasing means including a transversely curved, U-shaped fiat spring, said U-shaped spring being longitudinally curved beyond its buckling point, the initial radius of curvature of said transverse curve and the radius of curvature of said longitudinal curve being substantially the same, spring support means secured to said brush support and extending vertically upward from said brush 4 support, one leg of said U-shaped fiat spring being secured to the upper end of said spring support, an insulating pressure piece secured to the other leg of said U-shaped spring, said pressure piece overlying said brush and bearing thereon to urge said brush toward the pc riphery of said rotating member whereby constant pressure is applied to the brush throughout its useful life.

3. A brush holder for dynamoelectric machines, said brush holder comprising a brush support having a longitudinal opening formed therein adapted to have a brush arranged therein for longitudinal movement toward the periphery of a substantially cylindrical rotating member, a brush biasing means including a transversely curved, U-shaped flat spring, said U-shaped spring being longitudinally curved beyond its buckling point, the initial radius of curvature of said transverse curve and the radius of curvature of said longitudinal curve being substantially the same, spring support means secured to said brush support and extending vertically upward from said brush support, one leg of said U-shaped flat spring being secured to the upper end of said spring support, a conducting pressure piece secured to the other leg of said U- shaped spring, said pressure piece overlying said brush and bearing thereon to urge said brush toward the periphery of said rotating member whereby constant pressure is applied to the brush throughout its useful life.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain Aug. 2, 

